This invention relates to a system for controlling gasoline vapor emissions at a service station or stations where liquid gasoline is transferred from one container or tank to another, and more particularly to a simple and effective system for detecting liquid fuel blockages in the vapor return line of a fuel dispenser.
When a vehicle has consumed its supply of gasoline, its gasoline tank is full of gasoline vapors plus a lesser amount of liquid gasoline. During the process of dispensing a fresh supply of liquid gasoline into the tank, the vapor in the tank is displaced into the atmosphere. At the same time, fresh air is drawn down into the service station gasoline storage tank through provided vent pipes.
Gasoline vapors escaping into the atmosphere are a major source of smog and ozone. Fresh air, drawn into the storage tank, stimulates evaporation of the stored gasoline, which converts valuable gasoline into more polluting vapor.
The purpose of state of the art gasoline station vapor control systems is to solve both problems simultaneously; i.e. to prevent the escape of vapors from the vehicle tank and to prevent the ingestion of fresh air into the storage tank.
Because the volume of vapors escaping and the volume of fresh air ingested are approximately equal, the purpose of the system mechanism is to capture the vapors emitted from the vehicle tank and lead them through a conduit to the storage tank. As gasoline is dispensed from the storage tank, the storage tank ingests the vapor displaced from the vehicle tank instead of fresh air.
Pollution control agencies have increasingly mandated strict control standards for release of gasoline vapors into the atmosphere. For example, the California Air Resources Board (CARB) has mandated the following standards for vapor control systems which are identified as “Stage II vapor recovery systems”:                1) Highest vapor efficiency in all weather conditions;        2) Zero fugitive emissions (emissions of vapor through unmonitored openings or gaps in a gasoline delivery system);        3) Automatic continuous self-diagnosis;        4) System tolerant of leaks in service station hardware;        5) System simple, tough, reliable, and economical; and        6) System must use best available control technology.        
A system which meets the foregoing standards and qualifies as a Stage II vapor recovery system is currently manufactured by Hirt Combustion Engineers, Inc., of Pico Rivera, Calif., the assignee of the present invention, and is described in U.S. Pat. No. 6,193,500, which is herein expressly incorporated by reference.
In order to collect gasoline vapor displaced by refueling vehicles, auxiliary cans, motorcycles, and other vehicles and the like, a Stage II vapor recovery system 10 of the type shown in prior art FIG. 1 must have unobstructed, free flowing passages. When fuel is dispensed from a dispenser 11 to a vehicle 12, the vapor must travel unhindered from the vehicle fuel tank 13 through the dispensing nozzle 14, the coaxial hose 16, the vapor return piping 18, and then into the fuel storage tank 20. A common type of blockage is caused by liquid gasoline in the vapor passage of the coaxial hose 16. Spit-back, top-offs, condensation, and other inevitable operational problems can result in the presence of liquid fuel in the vapor path 21 of the hose 16. When the hose is draped, as is common during dispensing, and shown in prior art FIG. 2, a low point 22 is formed within the vapor path 21 that collects the entrained liquid. If enough liquid is entrained, the vapor path 21 becomes completely blocked. The blockage 23 does not allow the vacuum source to produce vacuum at the dispensing nozzle, as illustrated schematically in prior art FIG. 4. In FIG. 4, there is shown a dispensing nozzle 14 having a nozzle lever 15, which employs a plurality of holes 24 in the spout 26 thereof for collecting vapor generated by the dispensing process. For purposes of illustration, a first pressure gauge 28 having a needle 30 is disposed downstream of the blockage 23, and a second pressure gauge 32 having a needle 34 is disposed upstream of the blockage 23. As can be seen in the figure, the needle 30 in the first pressure gauge 28 is slightly above zero, indicating a slight positive pressure condition at the nozzle within the vapor passage 21, downstream of the blockage 23, while the needle 34 in the second pressure gauge 32 continues to indicate a vacuum condition in the vapor recovery system upstream of the blockage 23. This illustrates that the blockage has effectively prevented the nozzle portion of the system from remaining under a vacuum condition. Since the vacuum must reach the nozzle in order to force the collection of vapors in a “vacuum assist” type of system, this means that the system cannot meet vapor recovery specifications in the presence of such a blockage. As illustrated in FIG. 4, by arrows 35, when a vacuum condition is not maintained at the nozzle 14, fuel vapor as well as liquid fuel will inevitably spray outwardly from the nozzle into the surrounding environment.
A common method for removing excess entrained liquid 23 in the vapor path 21 is the use of a fluid-driven eductor 36, which is often called a “slurpy”, as shown in prior art FIG. 3. The slurpy 36 is typically constructed from a venturi 38 which is disposed in the product side or liquid fuel line 40 of the coaxial hose 16. The flow of liquid fuel, typically gasoline, through the venturi 38 during dispensing creates a vacuum. The vacuum pulls the entrained liquid 23 out of the vapor passage 21 and sends it into the product passage or liquid fuel line 40 through a bypass line 42. Thus, this LRD (Liquid Removal Device) causes the liquid fuel to be removed from the vapor path 21 and deposited into the fuel tank 13 of the vehicle 12 (FIG. 1).
However, a problem arises when the slurpy 36 cannot keep up with the rate that liquid fuel is entrained in the hose's vapor passage 21. A faulty slurpy, frequent spit backs, excessive tank top-offs, leaky fittings, and the like can all still permit liquid to fill the vapor path 21 and create a blockage 23.
Another prior art approach commonly employed is to conduct a V/L ratio test to ensure adequate vapor collection (i.e. blockage-free hoses). A flow meter measures the vapor returned, V, during a dispensing episode of L gallons. This test can be conducted with a portable vapor flow meter 44 connected to the spout end of the dispensing nozzle 14, as shown in prior art FIG. 5, or with a permanently installed vapor flow meter 46, which may be disposed in the base of the dispenser 11, as shown in prior art FIG. 6. The portable flow meter 44 allows only spot-checking because such an arrangement is cumbersome, time-consuming, and interferes with a customer's ability to dispense fuel. Additionally, it is difficult to perform, because of the need to dispense fuel to complete the test, requiring an adequate receptacle for receiving the dispensed fuel, and risking environmental damage in the event of a fuel spill, as well as release of fuel vapor to the atmosphere during the test. The permanent flow meter installation 46 is hidden in the dispenser cabinet and allows real time measurement during every fueling event. However, the permanent flow meter option requires a rather expensive low-pressure drop type flow meter, such as a Dresser Roots Meter, located in the base of each dispenser 11.
A problem arises when using the permanent flow meter approach, as shown in FIG. 6. Stage II systems employing “booted” nozzles will return only the vapor available at the vehicle tank fill neck 48. There is no excess air ingestion as with a bootless nozzle. A vehicle employing an Onboard Refueling Vapor Recovery System (ORVR) collects most or the all of the entire volume of vapor displaced during refueling. Thus, there is little or no vapor available to be collected by the booted nozzle. So the permanent flow meter measures little or no vapor collected (i.e. a V/L ratio close to or at zero is recorded). This scenario often signals a false alarm indicating the presence of a blockage 23.
An exemplary prior art V/L ratio test procedure is the California Air Resources Board (CARB) test procedure TP-102.5, the published specifications for which will be cited in a separate Information Disclosure Submission (IDS) in connection with the present patent application. It should be noted that, although the published test specifications reference the test as an A/L, or “Air to Liquid Volume Ratio” test, the “air” term is synonymous with the above referenced “vapor” term, and this is thus an example of the above referenced “V/L Ratio Test”. The CARB test is illustrated in FIG. 7. As noted above, in the discussion related to V/L testing procedures, this CARB test method involves pumping a measured volume of liquid gasoline, at a minimum rate, through the dispensing nozzle 14 into a test can 50 while measuring the air volume returning through the vapor recovery path 21 in the nozzle 14. One problem with this V/L test method is that it does not recover the gasoline vapor emitted from the test can 50 during the V/L test. The gasoline vapor, generated during the V/L test, escapes to the atmosphere. Also a risk of spillage exists because the gasoline must be dispensed into a test can 50 and then later returned to the storage tank 20 (FIG. 6).
The test equipment is also clumsy to use. Five separate components, which cannot be held in one hand, are required to perform the V/L test. These components include a spout adapter 52, a flow meter 54, which measures the volume of air ingested in the holes 24 in the spout of the nozzle 14, a hose 56, connecting the spout adapter 52 to the flow meter 54, the test gasoline can 50, and a timing device 58, such as a stop watch, for determining the flow rate. Also, the spout adapter 52, flow meter 54, and timing device 58 must be used in a very precise manner to ensure an accurate result, or the test will be invalid.
Additionally, the air ingested by the dispensing nozzle during the V/L test causes evaporation of the gasoline in the facility's storage tank. The evaporation of gasoline pressurizes the storage tank and causes fugitive gasoline vapor emissions. The liquid gasoline dispensed during the V/L test is returned to the gasoline storage tank after the test is completed. The return of the liquid gasoline from V/L testing to the gasoline storage tank also causes pressurization and hence fugitive vapor emissions.
What is needed, therefore, is a testing device which can, in a simple manner, without modification to the nozzle or dispenser, test to determine that the system vacuum is, or is not, present in the vapor return passage in the nozzle.